Open Data supplied by Natural Environment Research Council (NERC)

Niskin Bottle

The Niskin bottle is a device used by oceanographers to collect subsurface seawater samples. It is a plastic bottle with caps and rubber seals at each end and is deployed with the caps held open, allowing free-flushing of the bottle as it moves through the water column.

Standard Niskin

The standard version of the bottle includes a plastic-coated metal spring or elastic cord running through the interior of the bottle that joins the two caps, and the caps are held open against the spring by plastic lanyards. When the bottle reaches the desired depth the lanyards are released by a pressure-actuated switch, command signal or messenger weight and the caps are forced shut and sealed, trapping the seawater sample.

Lever Action Niskin

The Lever Action Niskin Bottle differs from the standard version, in that the caps are held open during deployment by externally mounted stainless steel springs rather than an internal spring or cord. Lever Action Niskins are recommended for applications where a completely clear sample chamber is critical or for use in deep cold water.

Clean Sampling

A modified version of the standard Niskin bottle has been developed for clean sampling. This is teflon-coated and uses a latex cord to close the caps rather than a metal spring. The clean version of the Levered Action Niskin bottle is also teflon-coated and uses epoxy covered springs in place of the stainless steel springs. These bottles are specifically designed to minimise metal contamination when sampling trace metals.

Deployment

Bottles may be deployed singly clamped to a wire or in groups of up to 48 on a rosette. Standard bottles have a capacity between 1.7 and 30 L, while Lever Action bottles have a capacity between 1.7 and 12 L. Reversing thermometers may be attached to a spring-loaded disk that rotates through 180° on bottle closure.

Sampling Strategy

Discrete chlorophyll and phaeopigment samples were collected by the Proudman Oceanographic Laboratory (POL), Liverpool on Oceans 2025 SO11 cruise 68 (PD10_10) in Liverpool Bay. The cruise ran from 28 to 30 April 2010 on the RV Prince Madog.

Originators Processing

Pre-processing: The test tubes were cleaned, paired up with screw-caps, numbered and placed in racks.

Sample collection: The filters were Whatman 0.7 µm pore size 47 mm diameter GF/F filters (straight from the box). Tweezers were used to handle the filters at the edges. Clean buckets were placed beneath the Niskin bottles on the CTD frame and the entire contents were taken. The samples were stirred before being measured out, typically 500 ml was required, less if turbid conditions. The pre-weighed filter was placed on to the holder and the funnel assembled. The vacuum pump was switched on and the suction carefully set to <0.2 bar The samples were added in stages and the filter was not allowed to go dry. The filter was then placed in a test tube, the cap was put on and then the tube was wrapped in aluminium foil, labelled and returned to the freezer at -18°C.

Post-processing: A fluorometric method was used: a chlorophyll standard was made and used to calibrate the fluorometer (Turner Designs, USA). The test tubes were taken out of the freezer and 5 ml of cold 90 % acetone was added. The foil wrapped tubes were then put in a polypropylene beaker with water and sonicated in the water bath for 15 minutes. The samples were not allowed to warm up and exposure to high light levels was avoided. The filters were removed from the pigmented acetone and analysed by the fluorometer as soon as was possible. A drop of 10% hydrochloric acid was added to convert chlorophyll to phaeophytin and the sample was then analysed again.

BODC Processing

The data were supplied to BODC as an Excel spreadsheet. This was converted to an ASCII format file for loading into the BODC database. Methodology and units were checked against information held in the BODC parameter dictionary and an appropriate parameter code was attributed to each variable.

Originator's Variable

Units

BODC Parameter Code

Definition of Parameter Code

Units

Comments

Chlorophyll -a concentration

µg l -1

CPHLFLP1

Concentration of chlorophyll-a {chl-a} per unit volume of the water body [particulate >GF/F phase] by filtration, acetone extraction and fluorometry

mg m -3

No conversion required as µg l -1 = mg m -3

CLSDFLP1

Concentration standard deviation of chlorophyll-a {chl-a} per unit volume of the water body [particulate >GF/F phase] by filtration, acetone extraction and fluorometry

mg m -3

Standard deviation values calculated by BODC

Concentration of phaeophytin-a

µg l -1

PHAEFLP1

Concentration of phaeopigments per unit volume of the water body [particulate >GF/F phase] by filtration, acetone extraction and fluorometry.

mg m -3

No conversion required as µg l -1 = mg m -3

PHSDFLP1

Concentration standard deviation of phaeopigments per unit volume of the water body [particulate >GF/F phase] by filtration, acetone extraction and fluorometry.

mg m -3

Standard deviation values calculated by BODC

The data and metadata fields were checked and then loaded into the database under the Oracle Relational Database Management System by matching the sample's station identifier and depth with the information already held in the database for this cruise. Where the data supplied included multiple replicates for each station, the mean value and standard deviation were loaded into the database. For single samples, the data were loaded without further modification. Data were then quality controlled by BODC and where suspect values were identified flags were applied.

Sustained, systematic observations of the ocean and continental shelf seas at appropriate time and space scales allied to numerical models are key to understanding and prediction. In shelf seas these observations address issues as fundamental as 'what is the capacity of shelf seas to absorb change?' encompassing the impacts of climate change, biological productivity and diversity, sustainable management, pollution and public health, safety at sea and extreme events. Advancing understanding of coastal processes to use and manage these resources better is challenging; important controlling processes occur over a broad range of spatial and temporal scales which cannot be simultaneously studied solely with satellite or ship-based platforms.

Considerable effort has been spent by the Proudman Oceangraphic Laboratory (POL) in the years 2001 - 2006 in setting up an integrated observational and now-cast modelling system in Liverpool Bay (see Figure), with the recent POL review stating the observatory was seen as a leader in its field and a unique 'selling' point of the laboratory. Cost benefit analysis (IACMST, 2004) shows that benefits really start to accrue after 10 years. In 2007 - 2012 exploitation of (i) the time series being acquired, (ii) the model-data synthesis and (iii) the increasingly available quantities of real-time data (e.g. river flows) can be carried out through Sustained Observation Activity (SO) 11, to provide an integrated assessment and short term forecasts of the coastal ocean state.

Overall Aims and Purpose of SO 11

To continue and enlarge the scope of the existing coastal observatory in Liverpool Bay to routinely monitor the northern Irish Sea

To develop the synthesis of measurements and models in the coastal ocean to optimize measurement arrays and forecast products. Driving forward shelf seas' operational oceanography with the direct objective of improving the national forecasting capability, expressed through links to the National Centre for Ocean Forecasting (NCOF)

To exploit the long time-series of observations and model outputs to: a) identify the roles of climate and anthropogenic inputs on the coastal ocean's physical and biological functioning (including impacts of nutrient discharges, offshore renewable energy installations and fishing activity) taking into consideration the importance of events versus mean storms / waves, river discharge / variable salinity stratification / horizontal gradients; b) predict the impacts of climate change scenarios; and c) provide new insights to Irish Sea dynamics for variables either with seasonal cycles and interannual variability, or which show weak or no seasonal cycles

To provide and maintain a 'laboratory' within which a variety of observational and model experiments can be undertaken (Oceans 2025 Themes 3, 6, 8, 9), including capture of extreme events

Demonstrate the value of an integrated approach in assessment and forecasting

Demonstrate the coastal observatory as a tool for marine management strategies through collaboration with the Environment Agency (EA), Department for Environment, Food and Rural Affairs (DEFRA), Joint Nature Conservation Commmittee (JNCC), English Nature (EN), Department of Agriculture and Rural Development (DARD), and Local Authorities, providing management information pertinent to policy (e.g. Water Framework Directive)

Please note:the supplied parameters may not have been sampled from all the bottle firings described in the table above. Cross-match the Sample Reference Number above against the SAMPRFNM value in the data file to identify the relevant metadata.